1. Field of the Invention
The present invention relates to a data conversion system and a data conversion method thereof and, more particularly, to a data conversion system adopted in a system for accessing the Internet from a portable information terminal based on WAP (Wireless Application Protocol) and a data conversion method thereof.
2. Description of the Related Art
System for accessing the Internet from a portable information terminal based on WAP is composed of a portable information terminal, a WAP proxy as a relay point between a wireless network and the Internet, a content filter for converting WWW (World Wide Web) contents into WAP contents and a Web server for providing WWW contents or WAP contents. When the portable information terminal makes a request for obtaining contents on the Web server, the contents on the Web server are obtained through the WAP proxy, and when the contents are WWW contents, they are converted into WAP contents by the content filter and then transmitted to the portable information terminal.
The conventional technique, however, has the following problems. The first problem is that conversion of contents by the content filter is not appropriate. In a case of such contents having a large volume of information as image data not directed to a portable information terminal, simply converting the format of the image data is not enough to enable a portable information terminal having a limited display capacity to use the data. Although it is possible to specify a portable information terminal to fixedly convert an image into an image optimum to the terminal, it is impossible in this case to cope with portable information terminals having different performances. The reason is that the contents filter is capable of conducting only fixed contents conversion processing.
The second problem is that in a case where appropriate contents need to be provided according to a client of a desktop personal computer, a portable information terminal and the like, it is necessary to prepare contents according to performance of each client such as a display capacity. The reason is that on the side of the WAP proxy and the Web server, automatic conversion of the contents using client information such as a display capacity is not possible.
On the other hand, one example of techniques of converting contents having a large volume of information into that appropriate for the portable information terminal is disclosed in Japanese Patent Laying-Open (Kokai) No. Heisei 11-250009 (hereinafter referred to as Literature 1). The technique disclosed in Literature 1 is directed to provision of Internet services enabling access to Web data with ease under mobile environments by obtaining page data from an Internet Web server in response to a request from each terminal device, based on resource information of a terminal device as a transfer destination, converting the obtained page data into data adapted to the terminal device in question and transferring the converted page data to the terminal device.
According to the technique recited in Literature 1, the Internet Web server converts data into data adapted to a terminal device based on resource information from the terminal device. According to the technique disclosed in Literature 1, accordingly, resource information is defined as fixed information upon connection of the terminal device to an Internet service provider (ISP) and the fixed resource information is adopted when resources on the Web server are to be designated (URL: Uniform Resource Locator). Therefore, even when a resource is designated on other Web server thereafter, the formerly adopted resource information will be adopted to make change of resource information difficult.
Unlike the technique disclosed in Literature 1, the present invention provides a technique enabling data conversion with resource data changed for each of various Web servers. Then, ease of updating of resource information enables suitable adjustment of communication traffic to adjust responsiveness at the connection of the Internet. Although other examples of techniques of this kind are disclosed also in Japanese Patent Laying-Open (Kokai) No. Heisei 11-306067 (hereinafter referred to as Literature 2) and Japanese Patent Laying-Open No. 11-328075 (hereinafter referred to as Literature 3), means for solving the above-described problems is disclosed neither in Literature 2 nor in Literature 3.